The properties of oral actinomycetes which affect the potential of these bacteria to participate in cell-cell interactions with other oral microorganisms are under investigation. Many of the patterns of cell-cell interactions between the oral actinomycetes and oral streptococci have been elucidated. Results from a recent investigation using freshly isolated oral streptococci and actinomycetes not only confirmed earlier results with stock strains from national culture collections but also revealed additional patterns of coaggregation reactions. Currently, an extension of the type of investigation which described the coaggregation patterns between oral actinomycetes and streptococci is being conducted with oral gram-negative isolates. A great deal of specificity between certain Actinomyces israelii isolates and oral Cytophage isolates has been observed. It is expected that further investigation of bacterial cell-cell interactions will lead to better understanding of the natural mechanisms required to maintain these oral microorganisms in their ecological niche.